It is well known in the prior art that printed circuit boards are a highly cost effective and space saving innovation when used in electrical devices. Prior to the advent of printed circuit boards, it was necessary to run individual wires between each component used in an electrical device. The advent of printed circuit board technology permitted manufacturers who repeatedly utilized the same complex circuit design in a high volume product, to eliminate the individual wiring of each component into the system, while providing an integral mechanical support for the circuitry. More particularly, a printed circuit board has numerous electrically conductive pathways imprinted on a dielectric substrate, most frequently a fiberglass reinforced phenolic or epoxy. The electrical components may then be attached to the printed circuit board with the conductive patterns on the board forming the electrical connections therebetween.
Heretofore, conventional methods of forming the electrical pathways of a printed circuit board were both expensive and time consuming. For example in one process, the dielectric substrate is coated over its entire surface with a sheet of conducting metal, such as copper or aluminum. This is generally accomplished utilizing an electroplating technique. The selected pattern or matrix, which will represent the electrical pathways between the components, is then cut into a cloth material such as silk. The cloth material, having the cut-out matrix, is then placed on the dielectric substrate which has been previously coated with the conducting material. An etch-resist ink is then rolled over the cloth, with the ink passing through the cut-out pattern and forming an inked matrix on the coated dielectric substrate. The above described method is a conventional silk screen technique. The inked and coated board is then subjected to light which causes the etch-resist ink to become acid resistant. The dielectric substrate is then treated with acid such that all the metal areas of the board not coated with the ink are etched away leaving just the matrix pattern. The ink itself may then be removed by conventional techniques thereby leaving the electrically conductive pathways formed on the printed circuit board.
In another method used in the prior art, a catalyst is placed on an uncoated dielectric substrate in the desired wiring matrix. The substrate is then immersed in a charged solution of copper ions, such that the electrical pathways are formed by electrodeposition in the areas where the catalyst was placed.
As can be seen, these methods are both time consuming and expensive. Not only are numerous steps needed to produce a printed circuit board in a conventional manner, but great amounts of conducting metal are needed for coating the entire dielectric substrate, or to provide an ionic solution.